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.NET TWAIN image scanner

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4.91 (224 votes)
12 May 2002Public Domain
Using TWAIN API to scan images

Sample Screenshot

Abstract

In Windows imaging applications, the most used API for scanning is TWAIN www.twain.org. Unfortunately, the new .NET Framework has no built-in support for TWAIN. So we have to work with the interop methods of .NET to access this API. This article doesn't explain this interop techniques, and good knowledge of the TWAIN 1.9 specifications is assumed! The sample code included doesn't present a finished library, only some essential steps for a minimal TWAIN adaption to .NET applications.

Details

First step was to port the most important parts of TWAIN.H, these are found in TwainDefs.cs. The real logic for calling TWAIN is coded in the class Twain, in file TwainLib.cs.. As the TWAIN API is exposed by the Windows DLL, twain_32.dll, we have to use the .NET DllImport mechanism for interop with legacy code. This DLL has the central DSM_Entry(), ordinal #1 function exported as the entry point to TWAIN. This call has numerous parameters, and the last one is of variable type! It was found to be best if we declare multiple variants of the call like:

[DllImport("twain_32.dll", EntryPoint="#1")]
private static extern TwRC DSMparent(
    [In, Out] TwIdentity origin,
    IntPtr zeroptr,
    TwDG dg, TwDAT dat, TwMSG msg,
    ref IntPtr refptr );

The Twain class has a simple 5-step interface:

class Twain
{
    Init();
    Select();
    Acquire();
    PassMessage();
    TransferPictures();
}

For some sort of 'callbacks', TWAIN uses special Windows messages, and these must be caught from the application-message-loop. In .NET, the only way found was IMessageFilter.PreFilterMessage(), and this filter has to be activated with a call like Application.AddMessageFilter(). Within the filter method, we have to forward each message to Twain.PassMessage(), and we get a hint (enum TwainCommand) back for how we have to react.

Sample App

The sample is a Windows Forms MDI-style application. It has the two TWAIN-related menu items Select Source... and Acquire... Once an image is scanned in, we can save it to a file in any of the GDI+ supported file formats (BMP, GIF, TIFF, JPEG...)

Limitations

All code was only tested on Windows 2000SP2, with an Epson Perfection USB scanner and an Olympus digital photo camera. The scanned picture is (by TWAIN spec) a Windows DIB, and the sample code has VERY little checking against error return codes and bitmap formats. Unfortunately, no direct method is available in .NET to convert a DIB to the managed Bitmap class... Some known problems may show up with color palettes and menus.

Note, TWAIN has it's root in 16-Bit Windows! For a more modern API supported on Windows ME/XP, have a look at Windows Image Acquisition (WIA).

License

This article, along with any associated source code and files, is licensed under A Public Domain dedication

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Comments and Discussions

 
QuestionWin 7 64bit problem? Pin
Edgar Rocha Carvalho13-Nov-10 17:24
memberEdgar Rocha Carvalho13-Nov-10 17:24 
AnswerRe: Win 7 64bit problem? Pin
m_cozza27-Apr-11 5:43
memberm_cozza27-Apr-11 5:43 
QuestionI want to show UI only,but not transfer the image to program. Pin
zouy9-Nov-10 2:33
memberzouy9-Nov-10 2:33 
Generalconvert from intpr to bitmap Pin
Tamer Hatoum4-Nov-10 12:56
memberTamer Hatoum4-Nov-10 12:56 
QuestionDuplex capabilty get "Failure" Pin
jymitra26-Oct-10 4:18
memberjymitra26-Oct-10 4:18 
Questionshow UI hang application(windows 7 64bit ) Pin
jymitra18-Oct-10 19:53
memberjymitra18-Oct-10 19:53 
AnswerRe: show UI hang application(windows 7 64bit ) Pin
kada12322-Oct-10 0:11
memberkada12322-Oct-10 0:11 
GeneralRe: show UI hang application(windows 7 64bit ) Pin
jymitra26-Oct-10 4:24
memberjymitra26-Oct-10 4:24 
hello ,,thanks for reply but i did it ..but problem is not about platform but shoUI not working ..
GeneralIssues with B/W andn using ADF Pin
Member 237557715-Oct-10 5:07
memberMember 237557715-Oct-10 5:07 
Generalscan Pin
zzahmadi14-Sep-10 10:40
memberzzahmadi14-Sep-10 10:40 
GeneralAttempted to read or write protected memory. This is often an indication that other memory is corrupt. Pin
flaviozoc27-Aug-10 5:09
memberflaviozoc27-Aug-10 5:09 
GeneralRe: Attempted to read or write protected memory. This is often an indication that other memory is corrupt. Pin
LupinTheThird30-Oct-11 11:11
memberLupinTheThird30-Oct-11 11:11 
QuestionAdd in my program ? Pin
circass28-Jul-10 6:51
membercircass28-Jul-10 6:51 
GeneralICAP_XFERMETH File + Duplex Pin
Rafael C A Ribeiro26-Jul-10 3:02
memberRafael C A Ribeiro26-Jul-10 3:02 
Generalits Urgent and Matter of JOB Pin
farrukhahmedqureshi26-Jul-10 2:37
memberfarrukhahmedqureshi26-Jul-10 2:37 
QuestionHow can i read the image directly into a picture box using vb.net Pin
AmitSood198521-Jul-10 0:20
memberAmitSood198521-Jul-10 0:20 
QuestionHow to take Snapshots automatically by time ? Pin
circass3-Jul-10 9:19
membercircass3-Jul-10 9:19 
GeneralGetting Capability Pin
obrien.james1-Jul-10 13:59
memberobrien.james1-Jul-10 13:59 
GeneralICAP_AUTODISCARDBLANKPAGES Pin
strzata28-Jun-10 20:50
memberstrzata28-Jun-10 20:50 
GeneralRe: ICAP_AUTODISCARDBLANKPAGES Pin
Member 421407311-Oct-10 7:58
memberMember 421407311-Oct-10 7:58 
GeneralBadImageFormat Exception Pin
Shishir Shukla28-Jun-10 20:35
groupShishir Shukla28-Jun-10 20:35 
GeneralRe: BadImageFormat Exception Pin
strzata28-Jun-10 21:00
memberstrzata28-Jun-10 21:00 
GeneralRe: BadImageFormat Exception Pin
m_cozza27-Apr-11 5:46
memberm_cozza27-Apr-11 5:46 
QuestionHow to conver this project to asp.net c# Pin
Supachai Prasertsit27-Jun-10 0:47
memberSupachai Prasertsit27-Jun-10 0:47 
Questionare we obliged to open form to make acquisition and other steps? Pin
richardeau25-Jun-10 2:56
memberrichardeau25-Jun-10 2:56 

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Article
Posted 16 Sep 2001

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